It has been observed that the majority of energy intensive processes are driven by the rates of the heat and mass transfer. Specific details of a particular application, such as the chemistry involved in drying a material, the temperature and specific properties of the material, the ambient conditions, the resulting water or solvent evaporation rates, and other factors affect the outcome of any drying and/or heating process. These factors also often dictate the speed of the process, which is sometimes critical, and the nature and size of the drying equipment.
The properties of the boundary layer formed next to the surface along which a fluid moves dictate the heat transfer rate at the surface and therefore the drying rate at the surface. Because of the effect of the boundary layer on the heat transfer rate, it can be argued—as Incropera/DeWitt do in their textbook “Fundamentals of Heat and Mass Transfer”—that heat transfer rates are higher for turbulent flow at a surface than for laminar flow at that surface. In modern heat and mass transfer practice, there are several methods to disrupt the boundary layer in order to produce more turbulent flow and therefore more heat transfer
One method of disrupting the boundary layer, in order to increase the heat transfer rate or for any other purpose, and therefore the drying rate of a wet surface, is to focus acoustic sound waves or oscillations such as ultrasonic waves or oscillations—and also heated air in various embodiments—at the surface of the material or coating being dried as shown in U.S. Patent Publication No. 2010-0199510 to Plavnik, published Dec. 12, 2010, which issued as U.S. Pat. No. 9,068,775 on Jun. 30, 2015, both of which are hereby incorporated by reference in their entireties. This aforementioned publication disclosed one method of drying with the assistance of an intense high frequency linear acoustic field.